/Engine/Source/Runtime/GeometryFramework/Public/Components/DynamicMeshComponent.h
it is invalid to call this function if (1) the mesh triangulation has also been changed, (2) triangle MaterialIDs have been changed, or (3) any attribute overlay (normal, color, UV) topology has been modified, ie split-vertices have been added/removed. Behavior of this function is undefined in these cases and may crash. If you are unsure, use Notify Mesh Updated.
virtual void NotifyMeshVertexAttributesModified ( bool bPositions, bool bNormals, bool bUVs, bool bColors )